Did you realize that designers and fine wines have something in common? They do. They both get better with age. At least that's what they say about wine. I only know it to be true about designers. But this is a point that one certainly can't overlook. If you're a good designer, then when you look at something you designed last year, last month or last week, you should always think, 'Man, I could make that look better." If you don't feel that way, then you've become stale and complacent. Sorry to break that to you. The bad news is, that that feeling will get worse. Look at something you did 3 years ago. Now 5.
Case in point, that's why a strong portfolio should be constantly updated and refreshed, removing old stuff and adding new. The good news is, as you mature and grow in your talent and abilities your design will grow with you. Why? Because you are getting more and more familiar with your tools. You no longer have to hunt around and figure out "what were those key strokes to transform?" No, now it's become second nature. It's muscle memory, reflex and automated response.
Don't misunderstand, a thorough knowledge of Photoshop does NOT automatically make you a good designer. However, a lacking knowledge will hinder your pieces. One cannot fully make use of their tools if they don't know them thoroughly and without that knowledge you cannot be truly creative.
So what about your design "style" how does it grow and develop? By watching others. Learning. Listening. Gleaning. We see design all around us. The good, the bad, the ugly. But what we choose to do with that knowledge is up to us. While you are on that constant journey seeking current designs, trends and new concepts, don't forget to intentionally feed yourself good design.
On that note, I'm going to list some of my favorite sites for seeking that rejuvenation:
All Design Types: